A retired US Navy admiral just laid out a major threat from North KoreaJames Stavridis, a retired US Navy admiral and former NATO commander, outlined the dangers of an electromagnetic pulse (EMP) attack from North Korea in a column for Bloomberg on Thursday.

Analysts have told Congress that an EMP attack could kill up to 90% of the US population if successful.

Stavridis writes that he believes that while President Donald Trump’s intended summit with North Korean leader Kim Jong Un is well intentioned and “right.”

However, he notes that the chances of North Korea fully denuclearizing is low, and that the nuclear weapons in North Korea’s possession are still extremely dangerous.

“What makes it so worrisome is not only the handful of nuclear weapons in the hands of a dictator who may be able to lob a few to Honolulu or even to Seattle,” Stavridis writes.

“We also need to consider North Korea’s ability to deploy one or two nuclear weapons at altitude over the continental US in order to create a devastating burst of energy called an electromagnetic pulse.”

Stavridis writes that an EMP attack could involve three phases after the detonation of a nuclear weapon over the United States. He labels these waves as E1, E2, and E3.

The E1 phase, is “a brief pulse that is particularly devastating to what are known as supervisory control and data acquisition systems,” like water treatment facilities, heating, ventilation and air conditioning, and manufacturing plants.

E2 is a smaller burst immediately after E1, and could be as short as a microsecond. Despite its short time it could still wreak havoc because its targets would have already had their protection weakened by the E1 wave.

The E3 pulse “could last several minutes and attack long-line systems such as the electric power grid by destroying substations across the nation.” The E1 and E3 waves present the biggest threats, according to Stavridis, and could “deprive large parts of the country of electricity for weeks, months, or even a year or two.”

A retired US Navy admiral just laid out a major threat from North Korea 1
In this Thursday, Aug. 10, 2017, file photo, a man watches a television screen showing U.S. President Donald Trump, left, and North Korean leader Kim Jong Un during a news program at the Seoul Train Station in Seoul, South Korea. North Korea has announced a detailed plan to launch a salvo of ballistic missiles toward the U.S. Pacific territory of Guam, a major military hub and home to U.S. bombers. If carried out, it would be the North’s most provocative missile launch to date. | Ahn Young-joon/AP

Stavridis’ column echoes a report given to Congress in October 2017.

“Airliners would crash killing many of the 500,000 people flying over North America at any given moment,” Peter Vincent Pry, a former CIA analyst and one of the report’s authors, told Forbes.

Pry added that the country’s food supplies would be decimated by radiation and up to 90% of the population would die within a year.

Stavridis notes that the affects of an EMP have not been fully studied because a test would darken large segments of the country. He also noted that there does not seem to be an agreement amongst analysts over how likely an EMP attack is, or how damaging it would be.

Still, Stavridis recommends that the US harden its defenses against such an attack, first finding ways to protect its ballistic missiles so that they can be used even after an EMP, in order to deter any such attack.

The US should also “increase its ballistic missile defenses against the ‘single shot’ attack that would use EMP,” Stavridis writes.

A North Korean EMP attack could come from either a ballistic missile or a satellite orbiting the Earth that has a nuclear warhead placed within it. One report even said that a warhead attached to a balloon could suffice.